Newer-generation magnetic resonance imaging (MRI) systems may generate and transmit individual radio-frequency (RF) pulse trains in parallel over different independent radio-frequency transmit channels. Individual RF signals are applied to the individual transmit channels (e.g., the individual rods of a whole-body antenna).
Parallel transmission techniques, however, may increase peak pulse power, giving rise to concerns regarding excessive exposure to RF energy. The RF energy from an MRI scan may cause heating of the tissue of a body. One measure of RF absorption is the specific absorption rate (SAR), which specifies the deposited power per unit mass (watts/kg) due to the RF pulse. Inhomogeneity of an RF field (e.g., generated by the whole-body antenna) leads to one or more local exposures (e.g., hot spots) where a majority of the absorbed energy is applied (e.g., local SAR). Maximum values for SAR are specified by safety regulations and are to be met both globally (e.g., power absorbed by the whole body, such as the head of a patient) and locally (e.g., power absorbed per 10 grams of tissue). For example, a standardized limit of 3.2 watts/kg applies to the global SAR of a patient, and a standardized limit of 10 watts/kg applies to the local SAR per 10 grams of tissue in the head of the patient, according to an International Electrotechnical Commission (IEC) standard. For patient safety, SAR is monitored over the course of an MRI scan. Prior art techniques for monitoring SAR may require a large memory footprint that is expensive.